Gap Year and Retaking

Hi,
I got a C in a level chemistry and biology last year.
How should I be revising now to get As and how long in advance of my exams should I start?
Thanks

Totally doable to go from a C to an A; it’s more about exam-style practice than just rereading notes.
Start now with little-and-often:
Past paper questions by topic (mark with the mark scheme)
Make a list of what you lose marks on, then revise + re-try
Use flashcards/blurting for definitions + processes
Don’t skip required practicals (easy marks if you know method, variables, improvements)
For timing: ideally begin proper, consistent revision 10–12 weeks before exams, then ramp up to timed full papers in the last 4–6 weeks. All the best with the Prep.